The present invention relates to apparatus for mixing air and fuel in an internal combustion engine.
It is known that the fuel for an internal combustion engine must be atomized and mixed with air in order to enable combustion to occur inside the cylinder.
In petrol engines, the air and fuel are usually mixed before they enter the combustion chamber by a carburetor or by an injector connected to a throttle body.
In certain types of apparatus for mixing air and fuel known to prior art, a throttle body has at its intake end a tapered pipe known in engine jargon as air choke or funnel. The air choke is designed to convey the air or the mixture of air and fuel through the intake pipe with the minimum of flow resistance.
Close to the inlet of the air choke, there is an injector which reduces the liquid fuel to a fine spray and enables it to be mixed with the air as the two components travel from the inlet to the combustion chamber.
In other apparatus of this type, the height of the air choke is variable in accordance with the revolutions per minute (rpm) at which the engine is running.
Indeed, the total length of the intake pipes, that is to say, the sum of the part inside the cylinder head plus the choke, is an important parameter that considerably affects volumetric efficiency and hence engine power.
Each rpm level corresponds to an optimum length of the intake pipes, once the other construction parameters, such as pipe and valve size and engine timing, have been defined.
Prior art, for example, patent DE-1 009 429, also teaches the use of mechanical, hydraulic or pneumatic mechanisms connected to the crankshaft to vary the length of the intake pipes and in particular of the final air choke.
In this kind of apparatus, the length of the pipes depends solely on engine rpm and the air chokes of all the cylinders are lengthened or shortened by the same amount by the same actuator.
The applicant has found that the above described type of apparatus for mixing air and fuel for internal combustion engines can be improved in many respects, especially to optimize engine performance.
Indeed, the air and fuel mixing apparatus described above does not allow the air chokes of the different throttle bodies to be changed independently of each other.
This is a disadvantage because not all the cylinders in an engine work in exactly the same way, especially if their configuration is not symmetrical, and therefore they should be optimized by using air chokes of different lengths.
A motorcycle engine, for example, is mounted in such a way as to minimize its transversal dimension, limiting the width, and hence the frontal cross section, of the motorcycle.
Thus, two- or four-cylinder V or L engines are mounted in such a way that the crankshaft is transversal to the longitudinal axis of the motorcycle. In a two-cylinder engine, one of the cylinders is in front of the other. The air chokes of the two cylinders therefore open at positions where the fluid dynamic conditions are different because the parts of the air box facing the air chokes have different shapes and/or are affected by different types of aerodynamic flow.
Moreover, in the apparatus of the type described above, it is not possible to set the optimum length of each pipe on the basis of engine operating parameters in play at any given moment.
The present invention has for an object to provide air and fuel mixing apparatus for an internal combustion engine where the intake pipes of at least two cylinders can be varied in length independently of one another.
Another object of the invention is to provide an air and fuel mixing apparatus for an internal combustion engine where the length of the intake pipes can be varied in accordance with a multiplicity of engine operating parameters.
The invention has for an object in particular to provide an air and fuel mixing apparatus which is designed to be mounted in an internal combustion engine and which allows the length of each intake pipe to be set according to the rpm and opening percentage of the butterfly valve at any given moment while the engine is running.
These objects, as well as others that emerge from the description below, are accomplished by an air and fuel mixing apparatus for an internal combustion engine as described in the claims below.